Plant residue is plant material that remains in a field following a particular growing season. Plant residue includes roots, stem, leaves and seed bearing or enclosing plant structures (e.g. pods, cobs and husks) originating from plants present in the field during the previous growing season (eg: seeded crops, volunteer species and weeds). In order to plant a new crop in a field, plant residue from the previous crop must first be dealt with.
When following conventional tillage practices, crop residue is typically buried by turning over the soil using, for example, a plow such as a mold board plow or a chisel plow, a disc harrow, a field cultivator, or another suitable field working implement.
Conventional tillage practices have been followed for centuries. However, in recent years, conventional tillage practices have fallen out of favor since the underlying soil exposed during turning is especially prone to erosion. Also, for economic reasons, it is desirable to make a minimal number of trips across a field.
Conservation tillage practices have been used to address the disadvantages of conventional tillage practices. When using conservation tillage practices, crop residue is minimally disturbed prior to planting and is typically left in the field unburied. Often, a crop is planted through the crop residue using no-till planting techniques and a no-till planting implement adapted for that purpose.
One such planting implement comprises a combination of a conventional planter and a coulter wheel assembly. There are several examples in the prior art of coulter wheels and coulter wheel assemblies that are used as part of no-till planting implements. U.S. Pat. No. 5,473,999, issued on Dec. 12, 1995 to Rawson et al., discloses three coulter wheels in a triangular arrangement. U.S. Pat. No. 5,957,217, issued on Sep. 28, 1999 to Gunnink, discloses a strip tillage apparatus comprising a pair of coulter wheels rotatably mounted on a walking beam which in turn is pivotally mounted on a frame for mounting on a tool bar of a draft vehicle. U.S. Pat. No. 5,462,124, issued on Oct. 31, 1995 to Rawson, discloses a dual coulter device having a pair of coulter wheels arranged in a staggered relationship for mounting on a single tool bar. U.S. Pat. No. 6,412,571, issued on Jul. 2, 2002 to Mcilhargey, discloses a coulter wheel assembly comprising a vertical shank having a coiled spring. U.S. Pat. No. 5,649,602, issued on Jul. 22, 1997 to Bruce, discloses a coulter wheel which has wavy acutely angled flutes for greater cutting performance.
However, when using no-till planting techniques, crop residue prevents the soil from drying and warming following, for example, a winter season having cold temperatures and much precipitation. A farmer is prevented from planting a crop until the soil is sufficiently dry and warm. Consequently, the planting of crops is delayed shortening the growing season and having a potentially adverse impact on crop yields.
A new form of conservation tillage has recently emerged wherein the soil is minimally disturbed prior to planting in order to allow air to penetrate the mat of crop residue. This technique is variously known as minimum tillage, residue management, soil aeration or seedbed aeration. A farm implement is used to cut the crop residue and penetrate a short distance into the surface of the soil while lifting the soil vertically to permit access of air to the soil. This farm implement is sometimes known as a vertical tillage implement. Examples of such an implement are the Turbotill™ sold by Great Plains Manufacturing and the Reel Till™ sold by McFarlane Manufacturing Company. These purpose-built minimum tillage implements comprise a frame and one or two rows of coulter wheels connected by a gang shaft that is rotatably mounted to the underside of the implement frame. The implements are designed to cut and size residue in preparation for planting a field, followed by a series of conventional leveling attachments, such as spike harrows (eg: Buster Bars™) and/or rotary harrows.
However, the foregoing purpose-built minimum tillage implements suffer from several disadvantages. Firstly, since the coulter wheels are mounted on a gang shaft, the spacing of the coulter wheels is close together and is not laterally adjustable. When a large amount of crop residue is present, crop residue can collect between adjacent coulter wheels so that they become plugged, impeding rotation of the gang shaft and causing crop residue to be pushed into a mound by the movement of the implement. Secondly, the gangs do not allow for deflection of individual coulter wheels in response to impact with obstacles, for example rocks, potentially resulting in damage to the coulter wheel, the gang shaft, or the implement. Thirdly, the implement is purpose-built and is only usable for residue management; thus, the farmer must bear the expense of an extra piece of equipment which lies idle most of the year.